The use of an infrared beam and associated photo sensor is well known for measuring the level of opaque liquids and solids. The devices of this type are generally limited to use with opaque liquids and solids and are not suitable for use with transparent materials.
In many applications, the detection of the level of a liquid or solid is required for materials which are either transparent or opaque.
An apparatus in the prior art which will detect transparent or opaque liquids is described in U.S. Pat. No. 3,636,360 issued Jan. 18, 1972. This technique is limited to liquids contained within tubes, and is not suited for application where the liquid is contained within a flexible plastic bag or other non-rigid container.
Thus, there exists a need for a device which can be used to detect the level of a transparent or opaque solid or liquid in a non-rigid container.